Augmented reality (AR) is a novel technique that seamlessly combines real-world information with virtual-world information. With AR, virtual simulations of tangible information (visual information, sounds, tastes, tactile feelings, etc.) that would be rarely experienced in a certain spatial or temporal range in the real world generated by digital signal processing, computer and other techniques are overlaid on real world and perceived by human senses so as to provide a sensory experience of augmented reality. The virtual objects are overlaid in real time on the same scene or space of a real environment.
It is a core objective of AR to simultaneously and synchronously present real-world information and virtual information in such a manner that the two kinds of information are overlaid and complement each other. In visualized AR, a dedicated display system including a head-mounted seeks to display a real-world scene and multiple computer-generated graphics synthesized therewith to a user's eyes in a synchronized manner so that the user can visually perceive that he/she is just in the real-world environment.
AR involves a variety of new techniques and means for multimedia, three-dimensional modeling, real-time video display and control, multi-sensor integration, real-time tracking and registration, scene fusion, etc. AR provides information different from what human beings can perceive in general.
A complete AR system is implemented by a set of tightly-coupled hardware components operating in a real-time manner as well as an associated software system. Head-mounted displays (HMDs) have a number of outstanding advantages such as portability and visual immersion. Therefore, in addition to their extensive use in virtual reality (VR) systems, they have also been adopted as the display means for AR systems where they are also called see-through HMDs. By how they operate, see-through HMDs are divided into two groups: optical See-through HMDs operating according to optical principles; and video see-through HMD based on video synthesis techniques.
FIG. 1 is a diagram showing the imaging principle of a video see-through HMD based on video synthesis techniques. As shown in the figure, a real-world image 1 captured by a camera 2 is combined with a virtual image generated by a computer graphics system, and the combined image is output to a display screen 3 of the video see-through HMD. However, this portable AR system is associated with some fundamental drawbacks, one of which is that there is an inevitable time delay between the real-world image 1 captured by the camera 2 and the image displayed on the HMD display screen 3, which constitute one of the causes of a viewer's vertigo. As shown in FIG. 1, a digitized image signal T0 displayed on the display screen 3 and seen by the user's eyes 4 is delayed by one or even more frames from the digitized image signal Tn of the real-world image 1 captured by the camera 2 for capturing dynamic scenes. In other words, the image T0 on the display screen 3 seen by the user's eyes 4 is the image of a dynamic real-world scene captured by the camera 2 a while ago, and it is impossible for image signal T0 and image signal Tn to be synchronized.